Schilke Standard Series Trumpet Mouthpiece in Silver Group II 15C4 Silver Standard Series Trumpet Mouthpiece in Silver Group II 15C4 Silver Few companies know more about mouthpiece manufacture, design and physics than the Schilke Company They make a complete line of excellent trumpet mouthpieces that work with any instrument but especially compliment their fine line of outstanding trumpets Cup Diameter (First number in label): cups range from shallow to deep in numeric order from low to high Cup Volume (First letter in label): volume ranges from A to E from small to large - A: Small; B: Medium-Small; C: Medium (Standard); D: Medium-Large; E: Large Rim Contour (Second number in label): rims range from roundest to slightly rounded in numeric order from low to high - 1: Roundest; 2: Simi-Round; 3: Standard; 4: Semi-Flat; 5: Slightly Rounded Backbore (Last letter in label): backbo... They make a complete line of excellent trumpet mouthpieces that work with any instrument but especially compliment their fine line of outstanding trumpets